Array antenna

ABSTRACT

To provide an array antenna which has both excellent directional characteristics and axial ratio characteristics without changing a substrate or dimensions, even when a frequency is changed. 
     A first sequential arrangement section (S 1 ), in which antennas are sequentially arranged from the left end section to the center section, and a second sequential arrangement section (S 2 ), in which antennas are sequentially arranged from the right end section to the center section, are symmetrically arranged.

TECHNICAL FIELD

The present invention relates to an array antenna in which a pluralityof planar antenna elements with perturbation are linearly arranged.

BACKGROUND ART

Conventionally, an antenna represented by a planar antenna withperturbation has characteristics in having a narrow axial ratio band andmaintaining a satisfactory axial ratio near the designed frequency, butin that the axial ratio characteristics significantly degrades when thefrequency shifts. This state is shown in FIGS. 15( a) and 15(b), whereFIG. 15( a) is a graph showing the axial ratio characteristics, and FIG.15( b) shows a polarization state at the respective frequency. Asapparent from the graph, the axial ratio is substantially 0 dB and issatisfactory at the designed frequency, that is, near the centerfrequency f0, but the axial ratio characteristic significantly degradesat f−, which is shifted to the − side, and at f+, which is shifted tothe + side, with respect to the center frequency. In the polarizationstate, circular polarization is obtained at the center frequency f0, butan elliptical polarization inclined to the left or the right is obtainedand the axial ratio is significantly degraded at f− and f+.

A sequential array antenna in which planar antennas with perturbationare sequentially arranged has been developed in recent years (see e.g.,paragraph 0027 of Patent Document 1). The sequential array antenna isarranged with a plurality of antenna elements, and is excited with eachantenna element rotated by 180/n (n=1, 2, 3, . . . ) and the phase alsochanged by 180/n (n=1, 2, 3, . . . ). For instance, as shown in FIG. 16,when the sequential array antenna is configured by linearly arrangingthree antenna elements, each having one power supply point and opposingcutouts (perturbation), each antenna element is arranged after beingmechanically rotated according to the following equation φ_(n)=(n−1)π/N(n: n^(th) antenna element, N: number of antenna elements, N=3 in thecase of three antenna elements).

In the sequential array antenna including N elements, a completecircular polarization is radiated irrespective of the polarization ofthe antenna elements in the broadside direction (direction orthogonal tothe arranging direction of the antenna elements) when the rotation ofequation φ_(n)=(n−1)π/N and phase deviation are applied to the n^(th)antenna element, so that satisfactory circular polarization andimpedance characteristics can be maintained over a wide band.

However, when using a frequency (communication channel) shifted from thecenter frequency, the directional characteristics of the sequentialarray antenna become as shown in FIGS. 17( a) to 17(d) and a problem inthat the directional characteristics change by the frequency arises. Inparticular, when controlling the directional direction as a phased arrayantenna in combination with a phase shifter, the beam direction changesby the frequency. This is particularly significant when thecommunication counterpart is a linear polarization as in RFID, and thereception area tends to change by the frequency. FIGS. 17( a) to 17(d)show the directional characteristics and the axial ratio characteristicsof the sequential array antenna, where FIGS. 17( a) and 17(b) show thestate of the beam when the frequency f+ is used, and FIGS. 17( c) and17(d) show the state of the beam when the frequency f− is used. Here,E_(θ) is the horizontal component of the circular polarization and E_(φ)is the vertical component, where in the cases of frequency f+ andfrequency f−, the beam direction is left and right opposite although thegain does not change and the axial ratio characteristics do not changein E_(θ) and E_(φ), and furthermore, change exists in E_(θ) and E_(φ)when beam shifted in combination with the phase shifter, as shown inFIGS. 17( b) and 17(d).

In a case of a general phased array antenna in which antenna elementswith perturbation having the same antenna direction are linearlyarranged as shown in FIG. 18, the directional characteristics do notdepend on the frequency but fluctuation in gain becomes large as shownin FIGS. 19( a) to 19(d). FIGS. 19( a) to 19(d) show the directionalcharacteristics of the phased array antenna, where FIGS. 19( a) and19(b) show the state of the beam when the frequency f+ is used, andFIGS. 19( c) and 19(d) show the state of the beam when the frequency f−is used. In the cases of frequency f+ and frequency f−, the gain isopposite although the front direction is being faced and change is notfound in the directional characteristics in both E_(θ) and E_(φ).Similar to the above, change exists in E_(θ) and E_(φ) when beamshifted.

In other words, if the sequential array antenna or the phased arrayantenna is configured using a planar antenna element in which theindividual antenna axial ratio band is low, the broadside directionmaintains satisfactory axial ratio characteristics over a wide bandregardless of the change in frequency but the directional directionfluctuates due to change in frequency in the sequential array antenna.In the phased array antenna, the directional direction does notfluctuate due to change in frequency, but the axial ratio fluctuates dueto change in frequency. Thus, the respective array antennas haveadvantages and disadvantages in the directional characteristics and theaxial ratio band.

The following method is known as a method for solving the problems ofthe background art. One method of improving the axial ratio band is amethod of thickening the thickness of the substrate that configures thearray antenna or lowering the substrate dielectric constant. However,the use of such a method arises other problems in that the size of theantenna becomes large and miniaturization cannot be achieved, themanufacturing cost increases, and the like. Another method of improvingthe axial ratio band is a method of providing the power supply point attwo regions, but such a method also arises a different problem in thatthe power supply circuit becomes complicating. In addition, a method ofincreasing the antenna element not only in the horizontal row but alsoin the vertical row in the sequential array antenna to obtain aso-called sequential sub-array configuration is known, but such a methodalso arises a different problem in that the size of the antenna becomeslarge. Therefore, if the above-described problems are solved with themethods of the background art, problems such as enlargement of theantenna size and complication arise, and a satisfying method for solvingis not yet proposed.

Patent Document 1: Japanese Unexamined Patent Publication No. 09-98016

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

The present invention has been devised to solve the problems describedabove, and an object thereof is to provide an array antenna in which aplurality of planar antenna elements with perturbation are linearlyarranged, the array antenna having both excellent directionalcharacteristics and axial ratio characteristics without changing asubstrate or dimensions even when a frequency is changed.

Means for Solving the Problems

The present invention is directed to an array antenna in which aplurality of planar antenna elements with perturbation are linearlyarranged, the array antenna including: a first sequential arrangementsection in which antenna elements are sequentially arranged from a leftend section to a center section; and a second sequential arrangementsection in which antenna elements are sequentially arranged from a rightend section to the center section; wherein the first sequentialarrangement section and the second sequential arrangement section aresymmetric.

The method of applying perturbation to the planar antenna elementincludes a method of loading a degeneracy separation element by cutout(slit) and the like to a linear polarization patch antenna. The planarantenna generates circular polarization by loading the degeneracyseparation element. When referring to “sequentially arranged”, thismeans that the antenna elements are arranged to satisfy φ_(n)=(n−1)π/N(n: n^(th) antenna element, N: number of antenna elements). Whenreferring to “symmetric”, this means a state in which the firstsequential arrangement section matches the second sequential arrangementsection when rotated 180 degrees and overlapped thereon.

The plurality of planar antenna elements with perturbation may beprovided in an even number or an odd number. If including an odd numberof antenna elements, the planar antenna element positioned at the centersection is commonly used by the first sequential arrangement section andthe second sequential arrangement section.

Each of the planar antenna elements with perturbation may be a circularpatch antenna or a square patch antenna.

The planar antenna elements with perturbation configuring the firstsequential arrangement section and the second sequential arrangementsection may be spaced at equal or unequal intervals. The interval ofeach antenna element may be an equal interval or an unequal interval,but the symmetrical relationship in which the first sequentialarrangement section matches the second sequential arrangement sectionwhen rotated 180 degrees and overlapped thereon needs to be satisfied.

Effect of the Invention

As described above, according to the present invention, provided is anarray antenna in which a plurality of planar antenna elements withperturbation is linearly arranged, the array antenna including a firstsequential arrangement section in which the antenna elements arearranged from the left end section to the center section and a secondsequential arrangement section in which the antenna elements arearranged from the right end section to the center section, and the firstsequential arrangement section and the second sequential arrangementsection being symmetric. Both excellent directional characteristics andthe axial ratio characteristics are obtained without changing asubstrate or dimensions even when a frequency is changed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1( a) and 1(b) are diagrams describing that a directionaldirection of an array antenna of the present invention is symmetric,where FIG. 1( a) shows the directional property on the right side andFIG. 1( b) shows the directional property on the left side.

FIG. 2 is a diagram describing that the directional direction of thearray antenna of the present invention is symmetric, schematicallyshowing the conditions therefor.

FIGS. 3( a) and 3(b) are diagrams describing that the directionaldirection of the array antenna of the present invention is symmetric.

FIG. 4 is a diagram describing that the degradation of the axial ratioimproved in the array antenna of the present invention.

FIGS. 5( a) and 5(b) are diagrams describing that the degradation of theaxial ratio improved in the array antenna of the present invention.

FIGS. 6( a) and 6(b) are schematic views showing the arrangementstructure of the array antenna of the present invention, where FIG. 6(a) shows the arrangement for odd number and FIG. 6( b) shows thearrangement for even number.

FIG. 7 is a schematic view showing the arrangement structure of thearray antenna of the present invention.

FIGS. 8( a) to 8(d) are graphs showing the directional characteristicsin the array antenna of the present invention shown in FIG. 7.

FIGS. 9( a) and 9(b) are graphs showing the axial ratio characteristicswhen the array antenna of the present invention is configured by threeantenna elements in comparison with the axial ratio characteristics of aconventional sequential array antenna.

FIGS. 10( a) and 10(b) are graphs showing the axial ratiocharacteristics when the array antenna of the present invention isconfigured by four antenna elements in comparison with the axial ratiocharacteristics of the conventional sequential array antenna.

FIGS. 11( a) and 11(b) are graphs showing the axial ratiocharacteristics when the array antenna of the present invention isconfigured by five antenna elements in comparison with the axial ratiocharacteristics of the conventional sequential array antenna.

FIGS. 12( a) and 12(b) are graphs showing the axial ratiocharacteristics when the array antenna of the present invention isconfigured by six antenna elements in comparison with the axial ratiocharacteristics of the conventional sequential array antenna.

FIGS. 13( a) and 13(b) are diagrams schematically showing thearrangement of the antenna elements configuring the array antenna of thepresent invention, where FIG. 13( a) shows a case for arrangement atequal intervals and FIG. 13( b) shows a case for arrangement at unequalintervals.

FIGS. 14( a) and 14(b) are graphs in which the axial ratiocharacteristics for FIGS. 13( a) and 13(b) are compared.

FIGS. 15( a) and 15(b) are diagrams showing the axial ratiocharacteristics and the polarization state when a frequency is changedin a conventional planar antenna with perturbation, where FIG. 15( a) isa graph showing the axial ratio characteristics, and FIG. 15( b) is adiagram showing a polarization state at the respective frequency.

FIG. 16 is an explanatory view showing a configuration of a conventionalsequential array antenna.

FIGS. 17( a) to 17(d) are graphs showing fluctuation in the directionalcharacteristics and the gain in the sequential array antenna shown inFIG. 16.

FIG. 18 is an explanatory view showing a configuration of a conventionalphased array antenna.

FIGS. 19( a) to 19(d) are graphs showing fluctuation in the directionalcharacteristics and the gain in the phased array antenna shown in FIG.18.

DESCRIPTION OF SYMBOLS

-   S1, S10, S11, S12 First sequential arrangement section-   S2, S20, S21, S22 Second sequential arrangement section-   10(1), 10(2), . . . , 10(n), 20(1), 20(2), . . . , 20(n) Antenna    element-   11, 21 Power supply point-   12, 22 Cutout (perturbation)

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described indetail with reference to the drawings.

In brief, the arrangement of antenna elements in a conventionalsequential array antenna is improved in an array antenna of the presentinvention based on the following theory so that both the directionalcharacteristics and the axial ratio characteristics are satisfactoryeven when a usage channel is changed.

The present inventors came to invent the array antenna of the presentinvention based on the following presumption. This will be described indetail below.

First, as shown in FIGS. 1( a) and 1(b), there is shown the electricfield intensity in a θ+ direction and a θ− direction when a beam isdirected in a broadside direction under the following conditions in aarray antenna in which a plurality of (N) antenna elements (antenna 1,antenna 2, . . . antenna N) are linearly arranged.

FIG. 1( a) shows the electric field in the θ+ direction, and theconditions thereof are as follows. Assume that an excitation amplitudein the θ (Theta) direction of each antenna element is E_(θn) (firstantenna element is E_(θ1)), a composite electric field in the θ+direction is E_(θ+), a directional gain of each antenna element is D(θ),a number of waves is k=2π/λ, and a spacing of the antenna elements is d.An excitation phase (φ) of each antenna element is the same. In thiscase, a composite electric field E_(θ+) is expressed with the following<equation 1>.

<Equation 1>

E _(θ+) =D(θ)·ΣE _(θ) {j[φ+kd·sin θ·(N−n)]}  [1]

Expanding the term of Σ yields:

E _(θ1) {j[φ+kd·sin θ·(N−1)]}+E _(θ2) {j[φ+kd·sin θ·(N−2)]}+ . . . +E_(θN)(j φ)   [2]

FIG. 1( b) shows a case in which the beam is directed in the θ−direction, and the conditions thereof are as follows. Assume that anexcitation amplitude in the θ (Theta) direction of each antenna elementis E_(θn) (first antenna element is E_(θ1)), a composite electric fieldin the θ− direction is E_(θ−), a directional gain of each antennaelement is D(θ), a number of waves is k=2π/λ, and a spacing of theantenna elements is d. An excitation phase (φ) of each antenna elementis the same. In this case, a composite electric field E_(θ−) isexpressed with the following <equation 2>.

<Equation 2>

E _(θ−) =D(θ)·ΣE _(θn) j[φ+kd·sin θ·(n−1)])   [3]

Expanding the term of Σ yields:

E _(θN) {j[φ+kd·sin θ·(N−1)]}+E _(θ(n−1)) {j[φ+kd·sin θ·(N−2)]}+ . . .+E _(θ1)(jφ)   [4]

In [4], expansion starts from the N term for easy understanding.

The condition of E_(θ+)=E_(θ−) needs to be satisfied to obtain asymmetrical beam pattern. In this case, the directional characteristicsD(θ) of the individual antenna element is D(θ+)=D(θ−), and thus,equations [2] and [4] need to be equal. In other words, equation [5]below needs to be satisfied.

E _(θ1) {j[φ+kd·sin θ·(N−1)]}+E _(θ2) {j[φ+kd·sin θ·(N−2)]}+ . . . +E_(θ1)(jφ)=E _(θN) {j[φ+kd·sin θ·(N−1)]}+E _(θ(n-t)) }j[φ+kd·sinθ·(N−2)]}+ . . . +E _(θ1)(jφ)   [5]

From equation [5],

E _(θ1) =E _(θN) and E _(θ2) =E _(θ(n−1)) and   [6]

need to be satisfied. That is,

E _(θn) =E _(θ(N−n+1))   [7]

need to be satisfied. The conditional equation [7] is schematicallyshown in FIG. 2. In this case, the excitation amplitude from the leftend section to the center section, and the excitation amplitude from theright end section to the center section are responded in order.

If the axial ratio of each antenna element configuring the array antennais a:b, as shown in FIG. 3( a), the amplitude in the X direction excitesa·sin(ωt). If tilted by γ, as shown in FIG. 3( b), due to thearrangement of the antenna elements, the amplitude c in the X directionis expressed with the following mathematical formula.

c=√{square root over ({(a·cos(−γ))²+(b·sin(−γ))²})}{square root over({(a·cos(−γ))²+(b·sin(−γ))²})}  [8]

If each antenna element is sequentially arranged, the arrangement ofeach antenna element is assumed to satisfy the following conditionalequation.

<Conditional Equation>

φ_(n)=(n−1)π/N (n: n ^(th) antenna element, N: number of antennaelements)

Assuming the arrangement (tilt) of the second antenna element withrespect to the first antenna element is Γ,

Γ=γ₂−γ₁ =π/N   [9]

is obtained,the arrangement (tilt) of the n^(th) antenna element is expressed as(n−1)·Γ.

From equation [8], the amplitude in the X direction (Eθ) of the n^(th)antenna element is expressed as E_(θ)=√{square root over(((a·cos(·(n−1)·Γ))²+(b·sin (·(n−1)·Γ))²))}{square root over(((a·cos(·(n−1)·Γ))²+(b·sin (·(n−1)·Γ))²))}[10], where (N−1)·Γ=0, π, 2π,. . . need to be satisfied, that is, a general formula (N−1)·Γ=m·π (mrepresents an integral multiple) needs to be satisfied in order to matchthe amplitudes of the first antenna element and the N^(th) antennaelement in equation [10] although E_(θn)=E_(θ(N−n+1)) needs to besatisfied from equation [7]. When such an equation is transformed,Γ=m·π/(N−1) is obtained, which equation does not match equation [9].Therefore, shift occurs in the directional direction in the conventionalsequential arrangement, and the directional direction is not symmetric.

The directional direction is symmetric if each antenna element isarranged in a special sequential arrangement, as will be describedbelow.

In other words, in the array antenna using the special sequentialarrangement, the antenna elements are linearly arranged as shown in FIG.2, and the antenna elements are sequentially arranged from the left endsection to the center section, that is, arranged after beingmechanically rotated according to the above equation φ_(n)=(n−1)π/N (n:n^(th) antenna element, N: number of antenna elements), and similarly,the antenna elements are sequentially arranged from the right endsection to the center section, so that the direction of the antennaelements is symmetric between the left side and the right side. Sucharrangement of the antenna elements is referred to as “specialsequential arrangement” in the present invention.

The condition therefor is to satisfy the following equation,

γ1=γN, γ2=γ(N−n), γ3=γ(N−2), . . . , that is,

γn=γ(N−n+1)   [11]

From equation [11] and equation [10],

Eθ₁=Eθ_(N), Eθ₂=Eθ_((N−1)), Eθ₃=Eθ_((N−2)), . . . is obtained, whichequation can be transformed to a general formula of

Eθn=Eθ(N−n+1), which matches equation   [7].

Equation [7] is a conditional equation for obtaining a symmetric beampattern in the array antenna, and thus a result in that the directionaldirection is symmetric is obtained by arranging the antenna elements inthe special sequential arrangement so as to satisfy equation [11]. Thisis the same theory in the Eφ direction, where the condition of equation[7] is always satisfied even when the axial ratio characteristics due tofrequency is changed.

The above description demonstrates that the directional directionbecomes symmetric and that the directional characteristics aresatisfactory when the antenna elements are arranged in the specialsequential arrangement in the array antenna.

The improvement of the axial ratio by such special sequentialarrangement will now be described below.

First, assuming the axial ratio characteristics of one antenna elementis a:b, as shown in FIG. 4, and the amplitude of the angle θ is c inFIG. 4,

c(θ)=√{square root over ({(a·cos(φ))²+(b·sin (φ))²})}{square root over({(a·cos(φ))²+(b·sin (φ))²})}  [12]

is obtained. The axial ratio is expressed as E(φMAX)=E(φMIN) whereE(φMAX) is the maximum electric field direction and E(φMIN) is theminimum electric field direction when the array antenna is configured bysuch an antenna element. In one antenna element, a:b (φ herein is therotation of φ=θ deg in the antenna coordinate system) is obtained.

If the polarization of each antenna element is in the state shown inFIG. 5( a), the electric field intensity of the angle φ of antenna 1 isE1(φ), and the electric field intensity of the angle φ of antenna n isEn(φ). If N antenna elements are arranged in the same direction (normalarray), the composite electric field E(φ) is expressed as below.

E(φ)=ΣEn(φ) (supplement of Σ: total of n=1 to N)

Since E1(φ)=E2(φ)= . . . =EN(φ), then

E(φ)=N·E1(φ)=N·√{square root over (((a·cos(φ))²+(b·sin(φ))²])}{squareroot over (((a·cos(φ))²+(b·sin(φ))²])}

Therefore, E(φMAX)=a·N(φ=0°, E(φMIN)=b·N(φ=90°. The axial ratio of thenormal array is thus a:b.

If a certain antenna element is tilted by γ_(n), the polarization ofeach antenna element becomes the state shown in FIG. 5( b). In thiscase,

E _(n)(θ)=√{square root over({(a·cos(φ·γ_(n)))²+(b·sin(φ·γ_(n)))²})}{square root over({(a·cos(φ·γ_(n)))²+(b·sin(φ·γ_(n)))²})}  [13]

is obtained. In the case of the special sequential arrangement,γn=γ(N−n+1) is obtained.

Therefore, the composite electric field in the φ direction is

E(φ)=E1(φ)+E2(φ)+ . . . +EN(φ)   [14]

Here, E(φMAX) is obtained when φ=γ1 or γ2 or . . . . γN. Here, if thetilt of the center antenna element is γt, γn=γ(N−n+1), and E(γ1)>E(γt)in the case of the special sequential arrangement. Thus, the aboveequation becomes, excluding γt, E1(γ1)=E2(γ2) . . . EN(γN), where ifφ=γ1,

$\begin{matrix}{{E({\varphi MAX})} = {{E\; 1} + {E\; 2} + {E\; 3} + \ldots + {{EN}\left( {\varphi = {y\; 1}} \right)}}} \\{= {a + \sqrt{\left\{ {\left( {a \cdot {\cos \left( {{\gamma \; 1} - {\gamma \; 2}} \right)}} \right)^{2} + \left( {b \cdot {\sin \left( {{\gamma \; 1} - {\gamma \; 2}} \right)}} \right)^{2}} \right\}} + \ldots + {a.}}}\end{matrix}$

(First and last terms are a since first antenna element and N^(th)antenna element have tilt in the same direction)

Furthermore, since γ1−γ2<0 or γ1−γ2>0 and a>b, then

√{square root over (((a·cos(γ1−γ2))^(z)+(b·sin(γ1−γ2))²))}{square rootover (((a·cos(γ1−γ2))^(z)+(b·sin(γ1−γ2))²))}<a

Therefore, E(φMAX)<a·N.

Similarly, E(φMIN) is obtained when φ=γ1±90° or γ2±90° or . . . γN±90°.If the tilt of the center antenna element is γt, γn=γ(N−n+1), andE(γ1±90)<E(γt±90) in the case of the special sequential arrangement.Thus, the above equation becomes, excluding γt, E1(γ1±90)=E2(γ2±90) . .. EN(γN±90), where if φ=γ1±90°,

$\begin{matrix}{{E({\varphi MIN})} = {{E\; 1} + {E\; 2} + {E\; 3} + \ldots + {{EN}\left( {\varphi = {y\; 1}} \right)}}} \\{= {b + \sqrt{\begin{Bmatrix}{\left( {a \cdot {\cos \left( {{{\gamma \; 1} \pm 90} - {\gamma \; 2}} \right)}} \right)^{2} +} \\\left( {b \cdot {\sin \left( {{{\gamma \; 1} \pm 90} - {\gamma \; 2}} \right)}} \right)^{2}\end{Bmatrix}} + \ldots + {b.}}}\end{matrix}$

(First and last terms are b since first element and N^(th) element havetilt in the same direction)

Furthermore, since γ1−γ2<0 or γ1−γ2>0 and a>b, then √{square root over({(a·cos (γ1±90−γ2))²+(b·sin(γ1±90−γ2))²})}{square root over ({(a·cos(γ1±90−γ2))²+(b·sin(γ1±90−γ2))²})}<b. Therefore, E(φMIN)<b·N.

Therefore, E(φMAX):E(φMIN)<a:b, whereby degradation of the axial ratiois proven to be reduced by the special sequential arrangement. With suchspecial sequential arrangement, the difference in the directionaldirection and the degradation of the axial ratio can be improved, inparticular, even when the usage frequency is shifted from the centerfrequency by the usage channel as in the RFID. The array antennaconfigured by the special sequential arrangement is the array antenna ofthe present invention.

A specific configuration of the array antenna of the present inventionwill now be described with reference to FIGS. 6( a) and 6(b). FIGS. 6(a) and 6(b) are diagrams schematically showing the arrangement structureof the array antenna of the present invention, where FIG. 6( a) shows acase in which the number of antenna elements is an odd number and FIG.6( b) shows a case in which the number of antenna elements is an evennumber.

The array antenna according to one embodiment of the present inventionis configured as in FIG. 6( a). In other words, the array antenna has aplurality of antenna elements 10(1), 10(2), . . . 20(1), 20(2), . . .that are linearly arranged, where each antenna element is a circularpatch antenna having one power supply point 11 or 21, and opposingcutouts 12 or 22 as perturbation. The structure of each antenna elementis all the same, and only differs in the antenna direction. The powersupply point 11 or 21, and the cutouts 12 or 22 are given a referencenumber only to the representative portion.

The array antenna includes a first sequential arrangement portion S1 inwhich a plurality of antenna elements 10(1), 10(2), . . . aresequentially arranged from the left end section to the center section,and a second sequential arrangement section S2 in which a plurality ofantenna elements 20(1), 20(2), . . . are sequentially arranged from theright end section to the center section, where the number of the wholeantenna elements is an odd number. In this case, the antenna element10(n) or 20(n) at the center section shown is commonly used by the firstsequential arrangement section S1 and the second sequential arrangementsection S2. The first sequential arrangement section S1 and the secondsequential arrangement section S2 are in a symmetrical relationship. Thesymmetrical relationship means a relationship in which the firstsequential arrangement section S1 matches the second sequentialarrangement section S2 when rotated 180 degrees and overlapped thereon.When referring to sequentially arranging each antenna element, thismeans that each antenna is arranged after being mechanically rotated tosatisfy the equation φ_(n)=(n−1)π/N (n: n^(th) antenna element, N:number of antenna elements).

As another embodiment, the array antenna of the present invention isconfigured by an even number of antenna elements, as shown in FIG. 6(b), where the structure of each antenna element is similar to thestructure of the antenna element shown in FIG. 6( a). In this case aswell, the array antenna includes a first sequential arrangement portionS10 in which a plurality of antenna elements 10(1), 10(2), . . . aresequentially arranged from the left end section to the center section,and a second sequential arrangement section S20 in which a plurality ofantenna elements 20(1), 20(2), . . . are sequentially arranged from theright end section to the center section, where the first sequentialarrangement section S10 and the second sequential arrangement sectionS20 are in a symmetrical relationship, which is similar to the above.

In such an array antenna, the directional direction does not fluctuateby the frequency and the axial ratio band also improves when configuringthe array antenna by arranging the antenna elements in the specialsequential arrangement. For instance, examining the directionalcharacteristics and the axial ratio band when the array antenna of thepresent invention is configured by arranging three antenna elements inthe special sequential arrangement, as shown in FIG. 7, the results areas shown in FIGS. 8( a) to 8(d). FIGS. 8( a) to 8(d) correspond to FIGS.17( a) to 17(d), and show the directional characteristics of the arrayantenna of the present invention shown in FIG. 7. As opposed to FIGS.17( a) to 17(d), the beam direction is directed substantially the frontdirection and the directional characteristics does not fluctuate bychange in frequency at both the frequency f+ and the frequency f−, asshown in FIGS. 8( a) and 8(c). The gain also barely changes atfrequencies f+, f−, and the axial ratio band is also improved. Even whenbeam shifted in combination with the phase shifter, the directionaldirection does not fluctuate by the change in frequency and the axialratio band is also improved, as shown in FIGS. 8( b) and 8(d).

Furthermore, the present inventors conducted a comparative experimentfor when the antenna elements are arranged in the conventionalsequential arrangement and for when arranged in the special sequentialarrangement of the present invention, with the number of antennaelements changed between three and six. The results are shown in FIGS.9( a) to 12(b). In all figures, the left side is for frequency f− andthe right side is for frequency f+, the vertical axis is the gain, andthe horizontal axis is the angle. The special Etheta and the specialEphi are for the array antenna of the present invention, and sequentialEtheta and the sequential Ephi are for the conventional sequential arrayantenna. With reference to such figures, non-symmetrical relationship isobtained and the characteristics of the Etheta, Ephi are inverted at +fMHz and −f MHz for the sequential array antenna, but symmetricalrelationship is obtained and the axial ratio characteristics is improvedcompared to the sequential array antenna for the array antenna of thepresent invention, that is, that in which the antenna elements arearranged in the special sequential arrangement.

The array antenna of the present invention having the above-describedconfiguration has the interval of each antenna element set to an equalinterval. The interval of the antenna elements may not necessarily be anequal interval. To prove this, the present inventors performed asimulation while changing the interval of each antenna element. Inperforming the simulation, the antenna elements were arranged as inFIGS. 13( a) and 13(b). FIG. 13( a) shows a case in which five antennaelements are arranged at equal intervals of 150 mm. FIG. 13( b) shows acase in which five antenna elements are arranged at equal intervals of180 mm between the antenna element 10(1) and the antenna element 10(2)on the left end section and between the antenna element 20(1) and theantenna element 20(2) on the right end section, respectively. Theantenna elements are arranged at equal intervals of 160 mm between theantenna element 10(2) and the antenna element 10(3) at the centersection and between the antenna element 20(2) and the antenna element20(3) at the center section, respectively, so that the antenna elementsare arranged at uneven intervals as a whole.

In both cases shown in FIGS. 13( a) and 13(b), the symmetricalrelationship needs to be satisfied in which the first sequentialarrangement section S11 or S12 matches the second sequential arrangementsection 21 or 22 when rotated 180 degrees and overlapped thereon.

The simulation results of the array antenna of the present inventionconfigured as in FIGS. 13( a) and 13(b) are shown in FIGS. 14( a) and14(b). Special Etheta and special Ephi are the simulation results ofFIG. 13( a), and special Etheta unequal and special Ephi unequal aresimulation results of FIG. 13( b). With reference to such simulationresults, it is apparent that the axial ratio characteristics can beimproved even if the antenna elements are spaced at unequal intervals.

1. An array antenna in which a plurality of planar antenna elements withperturbation are linearly arranged, the array antenna comprising: afirst sequential arrangement section in which antenna elements aresequentially arranged from a left end section to a center section; and asecond sequential arrangement section in which antenna elements aresequentially arranged from a right end section to the center section;wherein the first sequential arrangement section and the secondsequential arrangement section are symmetric.
 2. The array antennaaccording to claim 1, wherein the plurality of planar antenna elementswith perturbation are provided in an even number or an odd number. 3.The array antenna according to claim 1, wherein each of the planarantenna elements with perturbation is a circular patch antenna or asquare patch antenna.
 4. The array antenna according to claim 1, whereinthe planar antenna elements with perturbation configuring the firstsequential arrangement section and the second sequential arrangementsection are spaced at equal or unequal intervals.
 5. The array antennaaccording to claim 3, wherein the planar antenna elements withperturbation configuring the first sequential arrangement section andthe second sequential arrangement section are spaced at equal or unequalintervals.